Activated carbon is, of course, a valuable commodity which has a wide variety of uses in industrial and consumer applications. By-and-large, the more highly activated the carbon is, the greater will be its value in the marketplace, since its adsorptivity is directly proportionate to its level of activation. While products having surface area values of less than 400 square meters per gram do have limited utility as activated carbons, the most desirable materials have higher values, and preferably in the range of the about 600 to 900 square meters per gram. The present invention is directed to a method for the production of solid carbonaceous products having specific surface areas of at least 400 square meters per gram.
Heretofore, the most effective and widely used commercial techniques for producing activated carbon have employed a two-step procedure, in accordance with which the carbonaceous feedstock is first carbonized to produce charcoal or coke, following which that intermediate product is activated in a subsequent step carried out, for example, in an indirectly-fired rotary kiln or multi-hearth furnace. However, such an approach, as conventionally practiced, suffers from a number of disadvantages.
More particularly, since the second (activation) step of the operation is normally carried out at a location different from that at which the first is effected, there are not only transportation costs to consider but, most disadvantageously, there is a substantial waste of thermal energy associated with normal handling and movement of the hot char. This is especially unfortunate because the activation reaction is endothermic, and requires large quantities of heat, which must therefore be obtained from a supplementary source. It is also evident that a two-step process inherently involves undue handling of rather difficult and offensive materials, introducing added cost and inconvenience factors.
The prior art does provide suggestions that solid carbonaceous products can be produced in a single step, which products may, in some instances, be more-or-less activated. Exemplary prior art includes U.S. Pat. Nos. 1,524,784, to DeBartolomeis; 3,525,674 to Barnebey; and 4,145,256 to Bowen. However, as will be evident from the description of the instant invention hereinafter set forth, none of those patents discloses a method which affords the advantages realized by the practice of the present method. Thus, broadly stated, no prior art process known to applicants permits the production of good yields of highly activated carbonaceous products in a single-pass, continuous operation, while minimizing energy requirements, and doing so in a manner which is economical, uncomplicated, efficient and subject to ready control to vary the nature and the quality of the products obtained.
Accordingly, it is the primary object of the present invention to provide a novel method whereby highly activated, carbonaceous products can be produced efficiently and economically, with a minimum consumption of energy.
It is also an object of the invention to provide such a method which can be effected in a single step, and in a manner which is convenient and subject to ready control, so as to permit reproducibility and facile variation of the nature and quality of the products obtained.
Another object is to provide a novel method having the foregoing advantages, and which is capable of producing a dry, solid product at a relatively low temperature, thus permitting facile handling of the product and minimizing the need for subsequent operations in connection therewith.
A further object of the invention is to provide such a method, which is adapted to be carried out in a reaction system which is relatively simple and inexpensive to construct and operate.
Yet another object of the invention is to provide a novel method of the foregoing nature, in which the amount of steam introduced into the reaction vessel is miminized, and in which no external supply of fuel need be provided.